1. Field of the Invention
The present invention relates to a cross-connection device installed in a node of a transmission network for switching transmission paths.
2. Description of the Background Art
With the advent of highly information-oriented society, the demand for communication is rapidly increasing and is, moreover, diversifying and advancing. A telephone set, for example, is almost one of necessaries of life today. Further, the transmission of text and graphic data by, for example, a facsimile machine and the transmission of information by, for example, a data terminal are added to the transmission of speech and that of data, respectively.
A transmission network is a communication system which transmits information or command data so as to meet the above-stated communication demands. A prerequisite with the transmission network is the capability of transmitting a greater amount of information more rapidly over a longer distance and processing information freely. However, what is required of the transmission network is, above all, to secure the transmission paths for implementing communication which is now an everyday occurrence. It is likely that a transmission path is interrupted by an error that occurs in a circuit due to a natural phenomenon or an accident, by concentrated call origination, by a hardware error of an exchange, by unexpected hardware bugs ascribable to unusual environments, etc.
Under the above condition, a cross-connection device replaces the faulty transmission path with a bypass transmission path. Also, the cross-connection device selectively sets up a high-grade and a low-grade transmission path for particular purposes of communication, i.e., switches a bypass transmission path assigned to computer data communication and a more short-circuited transmission path assigned to speech transmission.
Installed in a node of a transmission path, a conventional cross-connection device has a map that stores connection information indicating to which of many output transmission paths each input transmission path should be connected, a memory in which the connection information is written, and a group of switches for connecting each input transmission path to any of the output transmission paths. The control over such constituents is, in many cases, implemented by software. The problem with the conventional cross-connection device is that since it has only a single memory, it cannot change the connection information stored therein immediately. Specifically, a memory has the writing operation thereof controlled on the basis of addresses and data and, therefore, cannot rewrite a large amount of data in a moment. Moreover, it has been customary to assign the control over the cross-connection device to a single system. This is undesirable in that when a software error occurs, for example, in the single system, the paths of the switches and, therefore, the signal paths are disturbed which brings about communication errors.